Fluid bed process for the acetoxylation of ethylene in the production of vinyl acetate

ABSTRACT

A fluid bed process for the manufacture of vinyl acetate from ethylene, acetic acid and oxygen comprising feeding ethylene and acetic acid into a fluid bed reactor through a first inlet, introducing the oxygen into the reactor through a second inlet, co-joining the oxygen, ethylene and acetic acid in the reactor in contact with a fluid bed catalyst to produce vinyl acetate. The particle size diameter of the particulate catalyst material has a range of 60% of the particles being below 200 microns (0.1 mm) with no more than 40% of the particles being below 40 microns (0.04 mm).

[0001] This application is a continuation-in-part of U.S. Ser. No.08/252,874 filed Jun. 2, 1994.

BACKGROUND OF THE INVENTION

[0002] Field of the Invention

[0003] The present invention relates to a fluid bed process foroxyacylation of olefins or diolefins. In particular, the presentinvention is directed to a fluid bed process for the production of vinylacetate from ethylene, acetic acid and an oxygen-containing gas in thepresence of a fluid bed catalyst. More particular, the present inventionis directed to a fluid bed process for the production of vinyl acetateusing a palladium-gold-potassium fluid bed catalyst.

[0004] The commercial production of vinyl acetate by reacting ethylene,acetic acid and oxygen together in the gas phase in the presence of afixed bed catalyst containing palladium, a promoter metal, and an alkalimetal acetate is known. Usually the fixed bed catalyst components aresupported on a porous carrier such as silica, zirconia or alumina. Thereare various patents such U.S. Pat. No. 3,759,839 and Great BritainPatent 1,266,623 which disclose the manufacture of vinyl acetateutilizing palladium-promoted catalyst. In each of these patents, mentionis made of using a fluid bed process. However, in neither of thesepatents is there any mention of any technique or aspect of fluid bedprocedures which would produce unexpected superior or economicallybeneficial results when compared to the fixed bed process. In fact, ineach of these references, the typical conditions under which the processis run are fixed bed conditions.

[0005] There are numerous disadvantages related to the process ofmanufacture of vinyl acetate in a fixed bed procedure. Some of thesedisadvantages are:

[0006] 1. The catalyst utilized continuously deactivates in the fixedbed reactor with time on-stream. This leads to a decline in vinylacetate production. Thus, the product and recovery system must bedesigned to handle the high initial vinyl acetate yields and as theyields of vinyl acetate decline, a portion of the product recovery trainis not utilized, thus, capital is wasted.

[0007] 2. The fixed bed catalyst experiences uneven temperaturesthroughout the length of the reactor. Catalyst exposed to excessivelyhigh temperatures usually experiences premature aging. Catalyst residingin zones below the desired operating temperature will not optimallyreact to produce the maximum amount of vinyl acetate.

[0008] 3. The per-pass conversion of ethylene is limited by the level ofoxygen which is fed into the fixed bed reactor. In a fixed bedoperation, the oxygen is premixed with the ethylene/diluent and aceticacid stream prior to entering the reactor. This complete feed mixturecomposition must be outside the flammability zone or the risk ofexplosion/fire results. Accordingly, the amount of oxygen which can befed into the reactor is limited by the flammability limits of themixture.

[0009] 4. The vinyl acetate reaction in a fixed bed is seriouslydiffusion limited. Accordingly, much effort has gone into designingcatalysts wherein the active components are located in a thin shell onthe surface of the particles. Fixed bed catalysts which have a uniformdispersion of active material throughout the particle typically producefar fewer pounds of vinyl acetate per pound of noble metal thanshell-type catalysts.

[0010] 5. In a typical fixed bed procedure, catalyst activator(potassium acetate) must be continuously added as the reaction proceeds.This means that the activator is added at the inlet to the fixed bedreactor to replace the activator which exits the reactor. This method ofaddition of activator results in a non-uniform distribution of theactivator upon the catalyst which, in turn, results in zones of lessactive and more active catalyst.

[0011] The fluid bed process of the present invention overcomes many ofthe disadvantages of the typical commercial fixed bed operation andachieves unexpected superior results compared to fixed bed processes.The advantages of the fluid bed process of the present invention will bemore fully described below.

SUMMARY OF THE INVENTION

[0012] It is the primary object of the present invention to provide afluid bed process for oxyacylation of olefins or diolefins.

[0013] It is a further object of the present invention to provide afluid bed process for the manufacture of vinyl acetate from ethylene,acetic acid, and oxygen.

[0014] It is still another object of the present invention to provide afluid bed process for the manufacture of vinyl acetate using a fluid bedpalladium-based or palladium-gold-potassium base catalyst.

[0015] Additional objects and advantages of the invention will be setforth in part in the description which follows and in part will beobvious from the description or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

[0016] To achieve the foregoing objects of the present invention, theprocess for manufacturing of vinyl acetate in a fluid bed reactorcomprises feeding ethylene and acetic acid into the fluid bed reactorthrough one or more inlets, feeding an oxygen-containing gas into thefluid bed reactor through at least one further inlet, co-joining theoxygen-containing gas, ethylene and acetic acid in the fluid bed reactorwhile in contact with a fluid bed catalyst material to enable theethylene, acetic acid and oxygen to react to produce vinyl acetate andrecovering the vinyl acetate from the fluid bed reactor.

[0017] In a preferred embodiment of the present invention the ethyleneand acetic acid are fed into the reactor as a gaseous mixture throughthe one or more inlets.

[0018] In another embodiment of the present invention, the oxygencontaining gas is feed to the reactor through more than one inlet.

[0019] In a further preferred embodiment of the present invention theethylene and acetic acid gaseous mixture contains oxygen below itsflammability limit in the mixture.

[0020] In another preferred embodiment of the present invention, thefluid bed catalyst utilized to practice the process of the presentinvention comprises a catalyst having the following formula: Pd—M—Awherein M comprises Ba, Au, Cd, Bi, Cu, Mn, Fe, Co, Ce, U and mixturesthereof, and A comprises an alkali metal or mixtures thereof (preferablypotassium). Typically, the weight percent of the palladium and alkalimetal in the catalyst are 0.1 to 5.0 wt % palladium, preferably 0.5 to2.0 wt %: alkali greater than 0 to 10 wt %, preferably 0.01 to 5 wt %.In addition, the weight percent of M may range from 0 to about 5 wt %,preferably greater than 0 to 5 wt %, especially preferred being 0.1 to 3wt %. The fluid bed catalyst is manufactured according to the proceduresset forth in copending patent application Ser. No. 08/252,800, AttyDocket No. MFE-P-7114, assigned to the assignee of the instantapplication and herein incorporated by reference.

[0021] In a further preferred embodiment of the present invention theamount of catalyst including other fluidizable solids (e.g. inertparticulates such as silica) present in the fluid bed reactor ismaintained at a level sufficient to allow for the dissipation of theheat generated during the reaction so as to allow the reaction toproceed without damage to the catalyst.

[0022] In a still further preferred embodiment of the present invention,the fluid bed catalyst contains at least 60% of the catalyst particlesat a diameter of below 200 microns (0.1 mm) and no more than 40% of theparticles possessing a diameter being less than 40 microns (0.04 mm).Preferably, the catalyst particle diameter range is at least 50% of theparticles being less than 100 microns (0.1 mm) and no more than 40% ofthe particles having a diameter being less than 40 microns (0.04 mm).

[0023] The operation of the fluid bed process of the present inventionovercomes some of the distinct disadvantages described previously in thecurrent commercial fixed bed operation to produce vinyl acetate. In thefluid bed process the catalyst is homogeneously continuously mixed inthe reactor resulting in significant improvement in the homogeneousaddition of the promoter even if it is introduced through a singleoutlet. Furthermore, the fluid bed operation allows for the continuousremoval of a portion of deactivated catalyst and continuous replacementof catalyst during operation. This results in a steady stateperformance. In addition, a fluid bed reactor is nearly isothermal bydesign which minimizes catalyst deactivation due to exposure toexcessive heat. Finally, in the fluid bed process of the presentinvention, typically, the oxygen is not mixed with the hydrocarbon untilboth are inside the reactor. Therefore, the catalyst is present when thefeeds first mix at reaction temperature and the reaction proceedsimmediately. This means that the oxygen partial pressure begins to dropat once. Alternatively, oxygen may be fed with a hydrogen-containing gasas in a typical fix bed operation while additional oxygen can be spargedinto the reactor via the separate inlet. This unique feature of thefluid bed process allows significantly higher levels of oxygen to besafely employed in the conversion of acetic acid and ethylene to vinylacetate without danger of flammability. The utilization of higher levelsof oxygen permit substantially higher levels of ethylene and acetic acidconversion than are possible in the fixed bed processes.

BRIEF DESCRIPTION OF THE DRAWING

[0024]FIG. 1 is a schematic illustration of the process of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] In general, the process of the present invention comprises themanufacture of vinyl acetate in a fluid bed reactor comprising feedingethylene and acetic acid into a fluid bed reactor, preferably in thegaseous state, through at least one inlet; feeding an oxygen-containinggas into the fluid bed reactor through at least one second inlet;co-joining the oxygen-containing gas, ethylene and acetic acid in thefluid bed reactor while in contact with a fluid bed catalyst to enablethe ethylene, acetic acid and oxygen to react to produce vinyl acetateand recovering the vinyl acetate from the fluid bed reactor.

[0026] The general schematic for the fluid bed process of the presentinvention for the acetoxylation of ethylene to produce vinyl acetate (orthe oxyacylation of olefins or diolefins in general) will now be setforth in detail with reference to FIG. 1.

[0027] Fluid bed reactor 7 containing a fluidizable microspheroidalcatalyst is equipped with cooling coils 9 which provide for heattransfer from the reactor. Entering reactor 7 through line 3 is amixture of ethylene and acetic acid. This mixture is dispersed withinreactor 7 via a grid or sparger (not shown). It should be understoodthat the mixture of ethylene and acetic acid can be partially suppliedby recycle of acetic acid and ethylene via line 31. In addition, oxygenmay be added to the stream sent in via line 3 provided that theconcentration of the oxygen in the stream is maintained below that whichresult in forming a flammable mixture.

[0028] Oxygen is fed into the reactor through line 1 as a separatestream and is dispersed in the reactor via a separate gas dispersiongrid or sparger (not shown). The oxygen may be added in pure form or asan admixture with inert gas such as nitrogen or carbon dioxide. Thisstream of oxygen may also be mixed with low levels of hydrocarbons suchas ethylene or acetic acid provided that, again, the mixture is stilloutside the flammability limits. Because the gas streams provided inlines 3 and 1 are never mixed prior to entry into the reactor and uponinitiation of the reaction by the catalyst in the reactor, no flammablegas mixtures are produced.

[0029] The gaseous effluents produced in reactor 7 are passed through acyclone and/or filter system 13 which separates any exiting solidcatalyst from the gaseous product produced. The catalyst is thenreturned to the reactor via line 15 or collected for metals reclamationthrough line 16. In a preferred embodiment new catalyst may be suppliedalong with the recycled catalyst through line 14. Furthermore, promotermaterial may be added completely or partially to the catalyst systemalong with the new catalyst through line 14 thereby eliminating orsupplementing the need to add promoter via line 5.

[0030] The gaseous reaction product stream exiting from the top ofcyclone or filter 13 goes to product separation unit 19 via line 17where a crude stream of vinyl acetate is recovered through line 21. Anyrecovery and purification procedure known in the art may be utilized,including those disclosed in U.S. Pat. No. 3,759,839 herein incorporatedby reference or Great Britain Patent No. 1,266,623. The remaining streamcontaining unreacted ethylene, acetic acid, carbon dioxide (and/or otherinerts), and oxygen is transported via line 20 for recycle to the fluidbed reactor. To prevent excessive accumulation of inerts includingcarbon dioxide in the recycle stream, a small slip stream may betransported via line 23 to an inert removal station 25 where inerts areremoved and transported via line 27 for disposal while the remainingrecycle stream is transported via line 28 back into line 31 for re-entryinto reactor 7. Fresh ethylene may be supplied to the recycle stream 31through line 29. Fresh acetic acid may be supplied through line 4 to therecycle stream for entry into reactor 7 via line 3.

[0031] The process is generally conducted at elevated pressures.Typically, pressures of 50 to 200 psig are used, preferably in the rangeof 75 to 150 psig. The reactor temperature can range typically from 100°to 250° C. with temperatures in the range of 135° to 190° C. being mostpreferred. In general, higher temperatures can more advantageously beemployed with lower pressures.

[0032] Gaseous feed concentrations of ethylene, acetic acid and oxygenmay vary. Typically useful ranges are as set forth below:

[0033] Ethylene—30 to 70%, preferably 35 to 65%, most preferably 40 to60%:

[0034] Acetic Acid—10 to 25%, preferably 12 to 22%, most preferably 15to 20%:

[0035] Oxygen—8 to 25%, preferably 9 to 15%.

[0036] The balance of the streams is composed of inert material such ascarbon dioxide, nitrogen, argon and helium. The primary restriction onthe feed composition is that the oxygen level in the effluent streamexiting the reactor be sufficiently low such that the gas stream exitingthe fluid bed reactor is outside the flammability zone. This level iscontrolled by the amount of oxygen in the feed, the extent of oxygenconversion within the reactor and the concentration of inert in theeffluent stream.

[0037] The following examples are set forth below only for purposes ofillustration of the present invention.

EXAMPLES Example 1 Preparation of Fixed Bed Catalyst as Reported in U.S.Pat. No. 5,185,308

[0038] A representative fixed bed catalyst of composition 0.91 wt % Pd,0.34 wt % Au, and 3.2 wt % K on KA-160 silica spheres (5 mm) wasprepared as follows.

[0039] The appropriate weights of Na₂PdCl₄ and HAuCl₄ were dissolved in8.7 ml distilled water and impregnated on 15 g KA-160 silica spheres.The wet solid was allowed to sit undisturbed for several hours. Anaqueous solution of sodium metasilicate was then poured onto the wetsolid. Again the solid was left undisturbed overnight. An aqueoussolution of hydrazine hydrate was then added to the solution coveringthe catalyst spheres. The wet solid was left undisturbed overnight. Thesolid was then drained and washed free of chloride with distilled water.The solid was dried at 60° C., the appropriate amount of potassiumacetate in aqueous solution was then impregnated upon the solid and thefinished catalyst was dried at 60° C.

[0040] Evaluation of this catalyst under the following conditions: Feed:C₂H₄:HOAc:O₂:He = 53.1:10.4:7.7:28.6 GHSV: 3850/hr Temp: 150° C. (at hotspot) Pressure: 115 psig Catalyst Charge: 2.50 g Catalyst Dilution: 30cc of 4 mm glass beads

Example 2 Preparation of Fluid Bed Catalyst

[0041] A catalyst with targeted composition corresponding to 0.90 wt %Pd, 0.40 wt % Au, 3.1 wt % K was prepared by the preferred method usingthe steps indicated above.

[0042] The Na₂PdCl₄ (8.57 g) and HAuCl₄ (2.18 g) were dissolved in 128 gof distilled water. This solution was then slowly added to 210 g of thespherical silica support (KA-160, Sud Chemie). The solution supportmixture was swirled and gently shaken to insure even coverage. Thismixture was allowed to sit for two hours at room temperature andessentially all the solution was absorbed into the support. A solutionof 15.1 g of sodium metasilicate dissolved in 252 g of distilled waterwas poured onto the impregnated support. This mixture was allowed to sitfor three hours. At this time 26.8 g of hydrazine hydrate was added andthe mixture was permitted to sit overnight. The solid spheres were thenwashed thoroughly with distilled water to remove chloride from thesolid. The solid was dried at 60° C. overnight, then the dried solidspheres were crushed. The crushed catalyst (200 g) was milled overnightwith 133.3 g of silica sol (30 wt % SiO₂) and sufficient water toprovide a millable consistency. The catalyst slurry was then spray driedto form microspheroidal particles. A portion of the microspheroidalsolid (15 g) was then impregnated with 0.75 g of potassium acetatedissolved in 10 g of distilled water. This solid was dried at 60° C.overnight. Microscopic examination of the finished catalyst indicatedwell-formed microspheroidal particles.

[0043] Evaluation of the catalyst was carried out in a 40 cc fluid bedreactor under the conditions specified in Example 1 except the catalystbed was composed of 7.5 grams catalyst diluted with sufficient inertsilica fluid bed support to produce a total bed volume of 30 cc. Anethylene conversion of 5.2% with 93.7% selectivity to vinyl acetate wasobtained, indicating that the preparation method employed was effective.

Examples 3-7 Effect of Process Variables on Fluid Bed CatalystPerformance

[0044] The catalyst prepared in Example 2 was tested in order todetermine the effect of oxygen feed concentration, space velocity andtemperature on performance. The percent ethylene fed was maintainedconstant and nitrogen fed was adjusted downward as oxygen or acetic acidlevels increased. The following observations were noted: TABLE I Example3 4 5 6 7 % O₂ Fed 7.7 15.4 15.4 15.4 15.4 % HOA_(c) Fed 10.4 10.4 15.810.4 10.4 T (deg-C) 160 160 160 160 170 GHSV 3080 3850 3850 3080 3080 C2= Conversion 6.0 7.4 7.7 8.5 10.2 (%) VAM 93.0 90.6 92.5 91.2 86.4Selectivity (%)

[0045] Table I set forth above shows that good selectivity andconversion are maintained over a wide range of feed conditions.

Example 8 Preparation of Fluid Bed Catalyst

[0046] Dissolved 6.80 g of Na₂PdCl₄ and 1.73 g of HAuCl₄ in 110 g ofdistilled H₂O and impregnated this solution on 200 g of KA-160 silicaspheres (5 mm). Allowed wet solid to sit for two hours then added asolution of 12.0 g of Na₂SiO₃ in 240 g of distilled H₂O, mixed gentlyand allowed solid to sit undisturbed for 2 hours. To this mixture wasadded 21.3 g of 55% hydrazine hydrate. This mixture was allowed to sitovernight. Drained solution from solid and washed solid with freshdistilled H₂O until negative test for chloride was obtained. Thecatalyst precursor spheres were then dried overnight at 60° C. 200 g ofthis catalyst precursor were crushed and mixed with 19.05 g crushedKA-160 (washed to remove Cl), 202.8 g of Snotex-N-30 silica sol (36 wt %solids), and sufficient water to provide a millable consistency to theslurry. This slurry was milled overnight, then spray dried. Themicrospheroidal catalyst particles were oven dried at 110° C. Elementalanalysis of this solid found 0.62 wt % Pd and 0.23 wt % Au.

[0047] Dissolved 1.66 g of potassium acetate in 13.5 g of distilled H₂Oand impregnated this solution of 15.85 g of the above microspheroidalparticles. After drying the solid contained 9.5 wt % potassium acetate.

Examples 9 through 12

[0048] A mixture of 14.5 g of the catalyst in Example 8 and sufficientfluidizable silica to provide 30 cc were placed in the fluid bed testreactor. The conditions and results are as follow: Example 9 10 11 12 %C₂H₄ fed 50.2 48.4 45.6 45.9 % O₂ fed 5.3 8.6 9.7 8.9 % HOAc fed 10.39.9 13.5 13.7 % N₂ fed 34.3 33.1 31.2 31.4 Total Flow 380.8 394.3 418.5415.9 Temp (C.) 156 157 165 158 Pressure (psig) 115 115 115 115 C₂H₄conversion (%) 12.9 17.5 20.5 16.2 VAM selectivity (%) 90.0 87.7 86.189.3

Example 13

[0049] A 16.0 g portion of the catalyst prepared in Example 8 wascalcined at 640° C. in air for 2 hours. To this calcined solid was added1.6 g of potassium acetate dissolved in 13.5 g H₂O. The catalyst wasthen dried at 60° C.

Examples 14 and 15

[0050] 16.05 g of the catalyst of Example 13 was mixed with sufficientinert microspheroidal silica to give 33 cc. This catalyst mixture wastested in a fluid bed reactor with the following results. Example 14 15% C₂H₄ fed 47.2 45.2 % O₂ fed 6.7 10.5 % HOAc fed 14.0 13.4 % N₂ fed32.2 30.9 Total Flow 405 422.5 Temp (C.) 154 168 Pressure (psig) 115 115C₂H₄ conversion (%) 11.1 16.9 VAM selectivity (%) 91.8 83.7

Example 16

[0051] A spray dried catalyst was prepared in the manner described inExample 8 except that it contained 17 wt % silica from the sol andlevels of palladium and gold reagents were increased to give 0.69 wt %Pd and 0.25 wt % Au (no potassium acetate). 16 g of this microspheroidalsolid was calcined 0.5 hours at 400° C. followed by 2 hours at 640° C.1.57 g of potassium acetate dissolved in 13.5 g of distilled H₂O wasimpregnated upon 15.0 g of the calcined solid. This final catalyst wasdried at 60° C.

Examples 17 through 19

[0052] 13.3 g of the catalyst of Example 16 was mixed with sufficientinert microspheroidal silica to give 30 cc. This catalyst mixture wastested in a fluid bed reactor with the following results. Example 17 1819 % C₂H₄ fed 47.9 45.6 44.8 % O₂ fed 5.1 9.7 11.1 % HOAc fed 14.2 13.613.4 % N₂ fed 32.7 31.0 30.6 Total Flow 399 419 426 Temp (C.) 151 158167 Pressure (psig) 115 115 115 C₂H₄ conversion (%) 11.5 15.5 18.7 VAMselectivity (%) 92.0 89.3 86.0

[0053] While the invention has been described in conjunction withspecific embodiments, it is evident that many alterations, modificationsand variations will be apparent to those skilled in the art in light ofthe foregoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications and variations as fall within thespirit and broad scope of the appended claims.

What we claim is:
 1. The process for manufacturing vinyl acetate in afluid bed reactor comprising feeding ethylene and acetic acid into thefluid bed reactor through one or more inlets, feeding anoxygen-containing gas into the fluid bed reactor through at least onefurther inlet, co-joining the oxygen-containing gas, ethylene and aceticacid in the fluid bed reactor while in contact with a fluid bed catalystmaterial to enable the ethylene, acetic acid and oxygen to react toproduce vinyl acetate and recovering the vinyl acetate from the fluidbed reactor.
 2. The process of claim 1 wherein the ethylene and aceticacid are fed into the reactor as a gaseous mixture through the one ormore inlets.
 3. The process of claim 2 wherein the ethylene and aceticacid gaseous mixture contains oxygen below its flammability limit in themixture.
 4. The process of claim 1 wherein the fluid bed catalyst hasthe following formula: Pd—M—A wherein M comprises Ba, Au, Cd, Bi, Cu,Mn, Fe, Co, Ce, U and mixtures thereof and A comprises an alkali metalor mixture thereof.
 5. The process of claim 4 comprising maintaining theamount of fluid bed catalyst material in said reactor at a volumesufficient to allow for the dissipation of heat generated during thereaction of the ethylene, acetic acid and oxygen-containing gas therebyenabling said reaction to proceed without damage to the fluid bedcatalyst.
 6. The process of claim 5 wherein said fluid bed catalystmaterial comprises a mixture of particulate catalytic material andparticulate inert material.
 7. The process of claim 6 wherein 60% of theparticulate fluid bed catalytic material has a particle size diameter ofbelow 200 microns and no more than 40% of the catalyst particles have adiameter less than 40 microns.
 8. The process of claim 1 wherein theratio of the sum of the ethylene, acetic acid to oxygen-containing gasentering is within the flammability limits for said mixture.
 9. Theprocess of claim 8 wherein the concentration of the ethylene in thecombined gaseous feeds entering the reactor is between 30 to 70 volumepercent.
 10. The process of claim 9 wherein the concentration of thegaseous acetic acid in the combined gaseous feeds entering the reactoris between 10 to 25 volume percent.
 11. The process of claim 10 whereinthe concentration of the oxygen in the combined gaseous feeds enteringthe reactor is between 8 to 25 volume percent.
 12. The process of claim1 further comprising recycling at least a portion of the unreactedacetic acid, ethylene and oxygen into the fluid bed reactor.
 13. Theprocess of claim 12 further comprising recovering at least a portion ofthe fluid bed catalyst material escaping the fluid bed reactor andrecycling said material into the fluid bed reactor.
 14. The process ofclaim 1 wherein the pressure ranges from about 50 to 200 psig.
 15. Theprocess of claim 14 wherein the temperature ranges from between about100° C. to 250° C.